1. Field of the Invention
The present invention relates to an optical apparatus capable of selectively supplying power from a drive source to a plurality of power transmission mechanisms.
2. Description of the Related Art
A conventional general planetary gear mechanism includes, as shown in FIGS. 32(a) and 32(b), a sun gear 101 which rotates by means of a certain power, an arm 102 which rotates about a shaft 108 common to the sun gear 101 independently of the sun gear 101, and a planetary gear 103, which is secured to the arm 102 by a shaft 107 for rotation with respect to the arm 102 against the resistance of a spring 106 and in mesh with the sun gear 101.
In the shown mechanism, the planetary gear 103 can turn (revolve) about the sun gear 101, and can also turn (rotate) on its axis.
Such a planetary gear mechanism is generally used for a switching mechanism for selectively transmitting power for winding or rewinding of film in a camera or the like. In the planetary gear mechanism, as shown in FIG. 33, the extent of revolution of the planetary gear 103 is not an angle of 360 degrees, and is limited by two gears: a gear 104 for transmitting power to a winding system and a gear 105 for transmitting power to a rewinding system. In practice, however, since the gears may bite into each other, the extent of revolution of the planetary gear 103 is limited by bringing the shaft 107 of the planetary gear 103 into abutment with a portion 109 or 110. In this arrangement, if the sun gear 101 rotates toward the left as viewed in FIG. 33, the planetary gear 103 meshes with the gear 105 to cause the gear 105 to rotate in the direction indicated by a solid arrow. If the sun gear 101 rotates toward the right, the planetary gear 103 meshes with the gear 104 to cause the gear 104 to rotate in the direction indicated by a dashed arrow. A number of states brought about by the above-described operation are enumerated below:
1) Whether power is switched to the gear 104 or 105 is determined only by whether the sun gear 101 rotates toward the right or the left.
2) Each of the gear 104 and the gear 105 to which power is transmitted rotates in one direction only. That is to say, two lines are available for force transmission.
3) During power transmission or if gear backlash occurs in the direction of power transmission, the abutment portion 109 is subjected to a force F-109 from the shaft 107. In the opposite case, the abutment portion 110 is subjected to a force F-110.
4) If the planetary gear 103 is switched from the gear 105 to the gear 104 while power is being transmitted to the gear 105 as shown in FIG. 33, the planetary gear 103 only rotation (left-handed rotation) immediately after the right-handed rotation of the sun gear 101 is started, until the backlash is removed and the force F-109 disappears. Subsequently, the planetary gear 103 starts revolution.
The reasons why only two lines are available for force transmission as described above in Paragraph 2) are:
a) Since the conventional planetary gear mechanism is arranged in such a manner that the extent of revolution of the planetary gear 103 is limited by the gear 104 and the gear 105 as shown in FIG. 33, it is impossible to mesh the planetary gear 103 with any gear other than the gear 104 and the gear 105.
b) The direction of rotation of either one of the gears 104 and 105 is the direction of power transmission, while the direction of rotation of the other is the direction in which the planetary gear 103 is switched. As a result, either one of the gears 104 and 105 can transmit a force in one direction only.
For the above reasons, the number of transmission lines of force is two.
To realize the number of transmission lines of force which is greater than two, a planetary gear mechanism such as that shown in FIG. 34 may also be considered. In the shown mechanism, a plurality of (four, in this example) gears 111a to 111d are disposed circumferentially, and the positional relation between each of the gears 111a to 111d, the sun gear 101 and the planetary gear 103 is selected so that they can be arranged in a straight line to prevent each of the gears 111a to 111d from hindering the planetary gear 103. Stoppers 112a to 112d each of which prevents the left-handed revolution of the planetary gear 103 are disposed in the vicinity of the respective gears 111a to 111d for movement toward and away from the planetary gear 103. In this arrangement, by causing the sun gear 101 to rotate toward the right, a gear with which the planetary gear 103 is to be meshed is selected from among the gears 111a to 111d, and by causing the sun gear 103 to rotate toward the left, the shaft 107 is brought into abutment with the associated one of the stoppers 112a to 112d so that force is transmitted to the selected one of the gears 111a to 111d. However, this arrangement merely solves the problem stated in paragraph a), and the problem of paragraph b) remains. The direction in which force can be transmitted to each of the gears 111a to 111d is limited to one direction only as shown in FIG. 34, and no force can be transmitted through rotation in the opposite direction.
However, the arrangement of FIG. 34 which uses four gears 111a to 111d and four gear trains which can be coupled to the respective gears 111a to 111d has a problem: Since force can be transmitted in one direction only, it is difficult to use the arrangement as a mechanism which requires rotation in both right-handed and left-handed directions. If there is a planetary gear mechanism which can transmit force in both right-handed and left-handed direction by means of one gear train, it is possible to selectively transmit power from a single power source to a plurality of gear trains by causing a sun gear to rotate toward the right or the left.
FIG. 35 shows a model diagram of the basic concept of such a planetary gear mechanism.
In the arrangement shown in FIG. 35, the revolution of the planetary gear 103 is stopped by an arbitrary one of stoppers 113a to 113d and the adjacent one of stoppers 114a to 114d, whereby both the right-handed and left-handed revolutions of the planetary gear 103 are stopped and power can be transmitted to the desired one of the gears 111a to 111d in either direction of rotation thereof.
Consideration will be given below to a case where, in such an arrangement, an element to which power is to be transmitted is switched, for example, from the gear 111a which is presently in mesh with the planetary gear 103 to the gear 111b. It is assumed that the direction of rotation of the output gear 111b after switching is desired to be made left-handed (the direction of rotation of the sun gear 101 is also made left-handed).
In this case, the sun gear 101 is made to rotate toward the right to cause the planetary gear 103 to revolve toward the right and mesh with the gear 111b. However, since it is desired that the direction of rotation of the output gear 111b be made left-handed, it is necessary to cause the sun gear 101 to rotate in the opposite direction (toward the left) after the gears 103 and 111b have meshed with each other. This means that at the time when the gears 103 and 111b mesh with each other, a driving force is instantaneously transmitted to the gear 111b in the direction opposite to the desired direction. At this time, if the gear 111b is coupled to, for example, a power transmission mechanism for effecting zooming, the angle of view will shift in the direction opposite the desired direction and a photographer will have a sense of incompatibility.
To realize the above-described mechanism, the following problems must also be solved.
1) It is necessary to design a mechanism in which while the planetary gear 113 is revolving to mesh with any one of the gears 111a to 111d, the stoppers 113a to 113d and 114a to 114d are made to move backward so as not to limit the revolution of the planetary gear 113.
2) If power transmission is performed or backlash occurs with the planetary gear 103 meshed with any one of the gears 111a to 111d, a force F-115 or F-116 will be generated and applied to the adjacent one of the stoppers 113a to 113d or 114a to 114d. Each of the forces F-115 and F-116 must be controlled so as not to influence the revolution of the planetary gear 103.
The state shown in FIG. 35 will be considered below. In FIG. 35, the gear 111a is being made to rotate toward the left, or the sun gear 101 is stopped with the gear 111a driven to rotate toward the left. During this time, the stopper 113a stops the shaft 107 from rotating around the sun gear 101 toward the left. To switch the line of power transmission, if the stopper 113a in that state is released by means of the mechanism mentioned above in paragraph 1), the planetary gear 103 will revolve independently toward the left by the force indicated by the arrow F-115. As a result, the control of the planetary gear 103 is hindered. For this reason, it is necessary to design a mechanism capable of controlling the revolving force of the planetary gear 103 without error.
FIG. 35 also shows the state wherein the driving force of the sun gear 101 which is rotating toward the left is being transmitted to the gear 111a. In this state, since none of the other gears 111b to 111d is meshed with the planetary gear 103, there is not a member which limits their rotation. In a case where an element to which power is to be transited from an arbitrary one of the gears 111b to 111d, for example, the gear 111c, is a mechanism which may be subjected to an external force by accident, for example, a zoom barrel mechanism in a camera, if a certain external force is applied to the zoom barrel mechanism from the outside of the camera, the zoom barrel mechanism will move independently. Of course, if the mechanism to which power is to be transmitted from the gear 111a is easily subjected to an external force by accident, when the planetary gear 103 revolves to another position after the completion of power transmission, a similar problem will arise.
In the arrangement shown in FIG. 35, the revolution of the planetary gear 103 is stopped by bringing any one of the stoppers 113a to 113d and 114a to 114d into abutment with the shaft 107, and the planetary gear 103 meshes with an arbitrary one of the gears 111a to 111d. The revolving force of the planetary gear 103, which is generated in the right-handed or left-handed direction during power transmission is cancelled by limiting the revolution of the shaft 107 in the same direction by means of the associated one of the stoppers 113a to 113d and 114a to 114d. In such an arrangement, if it is desired that the planetary gear 103 be made to mesh with another gear among the gears 111a to 111d by causing the planetary gear 103 to revolve toward the right or the left, it is necessary to cause the stoppers 113a to 113d and 114a to 114d to move backward so as not to limit the revolution of the shaft 107. In other words, a mechanism is needed in which none of the stoppers 113a to 113d and 114a to 114d interfere with the shaft 107 rotating around the sun gear 101. To realize such a mechanism, it is necessary to adopt one of the following arrangements:
A) An arrangement in which the stoppers 113a to 113d and 114a to 114d can move backward from the shaft 107.
B) An arrangement in which the shaft 107 can move backward from the stoppers 113a to 113d and 114a to 114d.
However, the arrangement of paragraph A) has the following disadvantages. Four pairs of stoppers must be operated, and if they are to be operated separately, a complicated construction is needed. If the four pairs are to be operated simultaneously, the size of the entire mechanism must be made large, with the result that the mass increases and the response of control deteriorates.
The arrangement of paragraph B) has also a number of problems. Since the shaft 107 rotates with the revolution of the planetary gear 103, the position of the shaft 107 during rotation must be detected. To operate a member which changes its position while rotating every moment, a complicated construction will be needed.
In the arrangement shown in FIG. 35, the revolution of the planetary gear 103 is stopped in such a way that the stoppers 113a to 113d and 114a to 114d which are arranged for movement toward and away from the shaft 107 are selectively brought into abutment with the shaft 107. However, if the stoppers 113a to 113d and 114a to 114d move backward and stops limiting the shaft 107, the revolution of the planetary gear 103 is not limited at all and the planetary gear 103 revolves unlimitedly as long as the sun gear 101 continues rotating. In such an arrangement, if it is desired to cause the planetary gear 103 to mesh with an arbitrary one of the gears 111a to 111d so that power transmission is performed with the revolution limited, it is necessary to use a device for detecting in which position the planetary gear 103 is revolving or which of the gears 111a to 111d is in mesh with the planetary gear 103. In this case, it is desirable to use a device capable of detecting the position of the planetary gear 103 during revolution as an absolute position. However, the number of such detecting devices must be increased according to the number of gears for power (in FIG. 35, four for the gears 111a to 111d), with the result that the complexity of the apparatus will increase.
For the above-described reasons, it is common practice to adopt a method of preparing a pulse disc (not shown) secured to an arm 102 or the shaft 107 and provided with a pattern of bright and dark segments provided and detecting the amount of rotation of the pulse disc by means of a photocoupler or the like, thereby solving the above-described disadvantages. More specifically, an arrangement adopting such a method makes it possible to reduce the number of parts used and also to use a simple detection method which merely detects "bright" and "dark" signals. The bright and dark segments may be formed so that the state where the planetary gear 103 is in mesh with any one of the gears 111a to 111d can be distinguished from the state where the planetary gear 103 is in mesh with none of the gears 111a to 111d.
In the above-described method of finding a position from the "bright" and "dark" signals, since a relative position is only detected, it is necessary to determine the first position (initial position) in advance, and this initial position serves also as a revolution abutment position beyond which the planetary gear 103 does not revolve.
Referring to the arrangement shown in FIG. 33, the revolution abutment position corresponds to the position where the planetary gear 103 is meshed with the gear 104 or 105. If the operation of bringing the planetary gear 103 into abutment with the gear 104 or 105 to find the initial position, the gear 104 or 105 may be rotated by accident at the revolution abutment position (initial position). It is necessary, therefore, to prevent such accidental rotation. Similarly, in the arrangement shown in FIG. 35, while the planetary gear 103 is making rotation with its revolution limited at the revolution abutment position, it is necessary to prevent the rotation from being transmitted to any of the gears 111a to 111d.
In the arrangement shown in FIG. 35, to detect the position of the planetary gear 103 during revolution, a method may be employed in which a pulse disc (not shown) provided with a pattern consisting of bright and dark segments is secured to the arm 102 or the shaft 107 and the amount of rotation of the pulse disc is detected by means of a photocoupler or the like. In this method, the number of parts can be reduced, and it is only necessary to detect "bright" and "dark" signals. The "bright" and "dark" segments of the pattern may be provided so that the state of the planetary gear 103 being meshed with any one of the gears 111a to 111d can be distinguished from the state of the planetary gear 103 being meshed with none of them. In the arrangement of FIG. 35, since the planetary gear 103 can selectively mesh with four gears, if the "bright" segments are made to correspond to the state of the planetary gear 103 being in mesh, four "bright" segments may be provided on the pulse disc. In a method of finding a position while detecting a relative transition such as a transition between brightness and darkness, it is necessary to determine the first position (initial position) as shown in FIG. 36. The sun gear 101 is made to rotate unconditionally during a predetermined time period in one direction to cause the planetary gear 103 to revolve, thereby bringing the shaft 107 into abutment with a revolution abutment member 117. The position at which the shaft 107 comes into abutment with the revolution abutment member 117 is determined as the initial position. (The revolution abutment member 117 may be provided not in the shown position but in any position, and any of the stoppers 113a to 113d and 114a to 114d can also be easily used as the revolution abutment member 117.) After the initial position has been determined, the amount of revolution of the planetary gear 103 is detected on the basis of the relative transition of a pulse signal and the planetary gear 103 is made to mesh with an arbitrary one of the gears 111a to 111d, and the rotation of the sun gear 101 is selectively transmitted to the meshed one of the gears 111a to 111d. In the above-described mechanism in which the revolution of the planetary gear 103 is controlled not sequentially in time but selectively while the position of the planetary gear 103 during revolution is being detected on the basis of the relative transition obtained from a pulse transition, the initial position is essential to the control of the revolution of the planetary gear 103. Accordingly, if, in each power transmission operation, power can be transmitted by bringing the planetary gear 103 into mesh with an arbitrary one of the gears 111a to 111d after the confirmation of the initial position, power transmission with improved reliability will be able to be realized.
However, if such "initial positioning" is performed each time an element to which power is to be transmitted is changed, since the "initial positioning" operation itself is not an actual operation for power transmission but a switching operation, a switching operation of extremely long time will be needed and no desired control will be not be able to be achieved; for example, the response speed of a photographic operation is impaired.
In general and in a camera provided with a power dividing device employing a planetary gear mechanism, after the completion of photography, a planetary gear is made to mesh with an output gear coupled to a film transportation mechanism and film is wound by an exposed frame. Subsequently, in general and, for example, in a camera provided with a zooming mechanism (or a focal-length varying mechanism which is switchable between two different focal lengths), the planetary gear is brought into mesh with the output gear coupled to the zooming mechanism in preparation for the next photographic cycle. However, in the case of a camera capable of continuous-shooting photography, if the above-described operation is performed, the response speed of a photographic operation is impaired.
It has conventionally been proposed to provide several kinds of systems capable of detecting an abnormality of a camera and inhibiting the operation of the camera or performing the same operation again.
In one typical example of such a system, if a position detecting means detects that shutter blades do not open, the subsequent shutter release operation is inhibited. In another example, if it is detected that a signal indicative of the feed of a perforation has not come during the automatic loading of a film, an error indication of the occurrence of an automatic-loading error is displayed.
In either example, the above-described operation is merely subjected to inhibition because the operation is a relatively simple operation and because when an error occurs in such an operation, even if the same operation is performed again, the probability that a similar error will occur again is extremely high.
Cameras provided with an increasingly large number of functions have recently been developed, and a complicated mechanism such as a zooming mechanism or a retracting mechanism may be incorporated or a mechanism for dividing power from a single driving source among various output elements may also be adopted for the purpose of making a camera body more compact. As a result, the sequence of operations has become more complex and attention has been drawn to the following two serious problems:
1) The length of the sequence increases, and hence the time period for the sequence to proceed from beginning to end becomes long. As a result, the influence of the outside world on a camera becomes serious and, for example, during the operation of the camera, an unduly large force may be applied to a zooming mechanism or the like by the application of an external force, or the probability that noise may be introduced into a control part becomes high.
2) With an increase in the complexity of each device, an operation error of a device which seldom takes place and hence may be ignored in a single-function apparatus becomes more and more serious. A typical example of the operation error is an operation error due to the biting of the teeth tips of a planetary gear and an output gear into each other.
In a conventional camera provided with an autofocus (AF) device, when a shutter button is pressed to its first stroke position, a distance measurement operation is performed. Then, when the shutter button is pressed to its second stroke position, a photographic lens is driven to move from its initial position to a desired position on the basis of the distance measurement information obtained from the distance measurement operation. Subsequently, the shutter is made to open and close, and further after the completion of the resetting operation of causing the photographic lens to return to the initial position, a film winding operation is performed.
In recent years, high-magnification zoom lenses have been incorporated into compact AF cameras of the type described above. Accordingly, to achieve a predetermined photographic resolution in such an AF camera, for example, if a stepping motor is used to drive the photographic lens, it is necessary to increase the number of driving steps in which the photographic lens is driven during AF driving, compared to a single-focus camera.
For this reason, there is a tendency for a longer time to be taken to set the photographic lens before a shutter opening and closing operation. This tendency naturally leads to the problem of a shutter time lag. In addition, since the driving sound of the stepping motor or the shutter is not too large in itself, there is no substantial driving sound due to a shutter release operation when the shutter button reaches the second stroke position. After the completion of the shutter opening and closing operation, the photographic lens is reset to the initial position, and when a film winding operation is started, the driving sound is generated for the first time.
Accordingly, in a considerably noisy circumstance, a photographer cannot hear a shutter release sound and often becomes uneasy about the state of the shutter release operation and the like. In other words, even though exposure is completed at the timing of the shutter opening and closing operation, the photographer hears the sound of a film winding operation and can feel that photography is completed. As a result, the photographer is afraid that the shutter release operation might have ended or the camera might have failed, and feels anxious during the period from the time he operates a shutter release button until he hears the sound of a film winding operation.
FIG. 35 shows the state wherein the driving force of the sun gear 101 which is rotating toward the left is being transmitted to the gear 111a. In this state, since none of the other gears 111b to 111d is meshed with the planetary gear 103, there is not a member which limits their rotation. In a case where an element to which power is to be transmitted from an arbitrary one of the gears 111b to 111d, for example, the gear 111c, is a mechanism which may be subjected to an external force by accident, for example, a focal-length varying mechanism in a camera, if a certain external force is applied to this mechanism from the outside of the camera, the mechanism will move independently. Of course, if the mechanism to which power is to be transmitted from the gear 111a is easily subjected to an external force by accident, when the planetary gear 103 revolves to another position after the completion of power transmission, a similar problem will arise.
To solve the above-described problem, after the completion of transmission, the planetary gear 103 may be made to selectively mesh with a gear which is coupled to a mechanism which is easily subjected to an external force by accident, and this meshed state may be held. However, the method of causing the planetary gear 103 to selectively mesh with the gear has the following problems:
In the arrangement shown in FIG. 35, the stoppers 113a to 113d and 114a to 114d serve to lock the revolution of the planetary gear 103, as described previously, and is arranged for movement toward and away from the planetary gear 103 and the shaft 107. It is assumed here that in a case where the planetary gear 103 is allowed to revolve with the stoppers 113a to 113d and 114a to 114d moved backward, the planetary gear 103 is made to mesh with the gear 111a to prevent idling of the mechanism coupled to the gear 111a, as shown in FIG. 36.
In this case, a device (not shown) detects that the planetary gear 103 has revolved up to and meshed with the gear 111a, and the stoppers 113a and 114a are made to move forward as shown, thereby locking the revolution of the planetary gear 103. At the moment the revolution of the planetary gear 103 is locked, it starts rotating. If the rotation of the sun gear 101 is stopped at the moment the revolution of 103 is locked, the rotation of the sun gear 101 causes the gear 111a to rotate. Accordingly, if the timing to stop the rotation of the sun gear 101 and the timing to perform locking of the revolution by the stoppers 113a and 114a are not accurately established, the mechanism coupled to the gear 111a will move if it is a "mechanism which is capable of functioning even during a state other than an abutment state".
A typical example of a mechanism utilizing only the abutment state is a mechanism utilizing a telephoto end or a wide-angle end, as in the case of the lens barrel of a bifocal camera. A typical example of the mechanism which is capable of functioning even during a state other than the abutment state is a mechanism capable of performing a zooming function even if the lens barrel is in the middle position other than the telephoto end and wide-angle end positions, as in a camera having a zooming mechanism.
If the planetary gear 103 is made to mesh with a gear coupled to the above-described zooming mechanism, at the moment the stoppers 113a and 114a for preventing idling engage with the shaft 107, the zooming mechanism may move accidentally. To prevent occurrence of such a problem, the rotation of the planetary gear 103 may be stopped before the locking of the revolution is started. This state is substantially identical to the state of the stoppers 113a and 114a being omitted, and it may be impossible to lock the zooming mechanism or to perform power transmission.